Macintosh SE/30 Faint chime and no video, possible short on +5V

[Ferrix97]

Hello

The Analog board is OK, I used another SE Board to test it and it works fine, I also installed the board in another SE/30 and it still shows the same issue: faint chime and no video (screen is totally black)

This seems to be a very early revision board, with the yellow-band capacitors.

I was looking at UE8 and I noticed that the resistance between +5V and GND is about 56 Ohms, which seems too low.

I then removed the capacitors and washed the board, now the resistance on J12 and UE8 is about 35 Ohms.

Soon I will solder new capacitors on the board, and measure the resistance again.

after washing the board (with the old caps still in place) The board produced a very faint chime, reset and interrupt also worked: I could hear the chime when I press reset and the sad mac tone when I press interrupt.

Once I recap the board, I will connect it to a Floppy drive and I'll see if it trie to read it.

Before I started working on the board, I took some photos, here are a few of them

 

[TheWhiteFalcon]

Likely both bad caps and damaged traces. The UE8 section looks more than a little gunky.

 

[Ferrix97]

Update!

just finished the recap, now the chime is loud and clear.

It seems like the machine is not booting from its hard drive

looking at the floppy port, +5 is 5.00V, +12 is 12.23V but -12V is 0.03V.

EDIT:

I hooked up an external SuperDrive with a copy of the NAD in it, apart from the "blip" that makes after you turn on the system, it does nothing.

 

[Ferrix97]

I just so happen to have it's original user manual, that also includes pinouts of the various connectors.

It seems like the -12V is not present on this model, so all of the voltages are OK.

I have no idea why it chimes but doesn't boot

 

[uniserver]

sounds like might be a bad floppy bourns filter, or bad scsi chip.. or bad lines to the scsi i/c.

 

[Ferrix97]

But even if the filters (which I have some of them in stock) and/or the SCSI IC are bad, the system should still show something on the display, right?

 

[uniserver]

nope. just a grey screen, with a mouse pointer, if the filter is bad.  or if no screen at all .. then that means UE8 is fried.

 

[Ferrix97]

the display remains totally black

I can borrow a hot air station from a friend, what is the best way and temperature to remove the chip?

 

[uniserver]

I set my hot air station at 575F

flux and tweezers? - not sure if that was your question.

 

[Ferrix97]

perfect!, thanks!

does the system start up if I only supply +5V using my bench power supply?

 

[max1zzz]

I can't talk for the se/30 specifically, But I suspect it will, I know the LC will start up with only the 5v supply

 

[Ferrix97]

took a quick look at the schematics: it looks like it needs at least +12V and +5V, -5V and -12V are used only on a few (serial?) chips and on the expansion slot

 

[360alaska]

It doesn't need -12v to boot but it does power the sound amplifier setup so you would get any internal sound...

 

[techknight]

the low ohms on 5V is actually normal, its the combination of the CPU and PALS loading down the 5V supply. 

 

[Ferrix97]

Update, I replaced UE8 (and lifted a pad in the process of doing it) but the problem is still there.

I repaired the lifted pad and all of the connections seem to mach the ones on the schematic.

 

[uniserver]

Wow looks like you have a couple of problem se/30's.

where are you getting your UE8 from?   LC166 or HC166?

these things go bad a lot.  so sometimes, you can take one from a "parts" board,  and its actually already bad.

 

[uniserver]

also swap your video rom with the other board just for giggles.

 

[Ferrix97]

The video roms are not the problem, I swapped them and both SE's still show the same problems.

Swapping the roms was one of the things I've tried, I found out that sometimes, the roms in a ceramic package loose their content. (I've spent ages troubleshooting an IBM XT Clone only to find this out...)

UE8 is a new part, it is a SN74LS166AD from TI, I bought it here

 

[Ferrix97]

I found out that the interrupt key produces a sad mac chime only if you press it after the startup chime, if you wait more that 6-10 seconds it does nothing

on the other hand, the reset button always works

I tried the same thing with the other board (the one with half video) and no matter when you press it (with no drives hooked up), it always makes a sad mac chime (that ends with 13, if I remember correctly)